This invention relates generally to an electrostatographic printing machine, and more particularly concerns a control device which regulates the concentration of toner particles in the developer mix.
Many types of systems have been developed to adjust the concentration of toner particles in the developer mix. These systems generally monitor the concentration of toner particles in the developer mix and furnish additional toner particles thereto as required. The density of the resultant copy is optimized by maintaining the toner particle concentration within the developer mix at a preferred value.
Dispensing systems usually do not furnish constant quantities of toner particles into the developer mix of the development system. This is particularly true of a vibrating system where the dispense rate varies as a function of the level of toner particles in the container.
Control systems sense the concentration of toner particles within the developer mix and produces an electrical signal indicative thereof. Exemplary systems of this type are described in U.S. Pat. No. 3,754,821 issued to Whited in 1973 and U.S. Pat. No. 3,778,146 issued to Knapp in 1973. As disclosed therein, an electrically biased transparent electrode, disposed on a photoconductive surface, passes through the developer mix. While in the development zone, the transparent electrode attracts toner particles from the developer mix. The electrode is thereafter illuminated, the intensity of the light rays passing therethrough being indicative of the concentration of toner particles within the developer mix. A photosensor detects the intensity of light rays passing through the transparent electrode and develops an electrical signal proportional thereto. The electrical signal is compared with a reference and a control signal is developed to actuate the toner particle storage container. If required, the toner particle storage container dispenses additional particles to the developer mix. Thus, when the concentration of toner particles is beneath a specified level, additional toner particles are always supplied to the developer mix. Contrawise, if the toner particle concentration level is above the predetermined level, no request for toner particles is received and additional toner particles are not furnished to the developer mix. Systems of this type are not usually critically damped and may hunt about the desired toner particle concentration level. An attempt to overcome the foregoing is described in U.S. Pat. No. 3,873,002 issued to Davidson et al. in 1975. As described therein, the electrical output signals from the photosensor are processed by a hard wired or a nonvariable program which establishes the sequence of dispensing toner particles to the developer mix. Thus, toner particles are only added to the developer mix, when a predetermined number of dispense requests are received. However, an inherent disadvantage to the foregoing is that the program is fixed. Thus, it may be difficult to employ the same program with differing machine configurations.
Accordingly, it is a primary object of the present invention to improve electrophotographic printing by utilizing a programmable control device so that the scheme for dispensing toner particles may be readily varied.